The proposed research will investigate the disturbances in immunoregulation of cell mediated immunity that are associated with human and experimental murine leprosy. Studies will be directed to analyses of feedback or inhibitory immunoregulatory mechanisms that may be operative in these diseases. The three cell types basic to generation of the immune responses, i.e., T-lymphocytes, B-lymphocytes, and macrophages will be tested for possible immunosuppressor activity. The mixed leukocyte reaction, measurement of cell mediated lympholytic activity, and the Mishell-Dutton cell culture system will be employed for detection of possible suppressor cell activity and should such be found, the nature of this activity will be explored in detail.